Welding apparatuses of this general type are known in the art and are used for welding foils, tarps and other flat materials made from plastic. Thus, the plastic webs are plasticized by introducing heat into an overlap portion of their edges and are subsequently compressed under pressure.
The patent application EP 1 900 501 A1 discloses a welding apparatus for connecting laterally overlapping gasket webs along their edges. The welding apparatus includes a frame that is displaceable by running rollers and a heating device supported by a support frame of the chassis and configured to melt the plastic webs that are to be welded. The plastic webs are pressed together by compression and feed rollers that are supported at the support frame and driven by a drive unit that includes at least one motor and at least one transmission. Additionally devices for moving the at least one upper pressing and feed roller relative to the lower fixated pressing and feed roller are provided which include a tensioning device for the at least one pivotably supported upper pressing and feed roller. Thus, for example during overlapping welding of plastic webs the individual webs have to be arranged overlapping at an intended seam and fixated. Furthermore the provided heating device has to be inserted between the edges of the webs that are to be welded together and a joining pressure has to be applied. Thus, replacing the pressing and feed rollers is required quite frequently depending on a desired seam geometry and a degree of contamination of the running surface. This replacement is often made more difficult by the heating device which is arranged proximal to the pressing and feed rollers.
In the field of the invention reference is also made to the printed documents DE 297 19 434 U1, DE 297 19 436 U1 and DE 77 00 687 U1.
DE 297 19 434 U1 discloses a welding apparatus for overlapping welding of foil edges, the welding apparatus including a heating element over whose heating surfaces the foil edges can be run in order to provide classification, wherein the heating element is suspended freely movable, essentially movable in a spring elastic manner perpendicular to the heating surfaces of the heating element, wherein the heating element is suspended at least at one leaf spring arm which extends essentially in a direction of the provided movement direction of the foil edges so that the heating element is pivotable about a parallel axis that is oriented transversal to and intended movement direction of the foil edges. Thus, the heating element is in particular suspended in a spring elastic manner so that it is already arranged in a substantially optimum position for feeding the foil edges when the heating element is not under load so that the at least one leaf spring extends essentially horizontally with its flat sides. The self-acting optimum adaptation is then provided based on the contact pressure of the foil edges against the effect of the spring which is rather weak. By the same token the at least one leaf spring is clamped at the feed side and extends to the output side wherein the heating element is supported at a free end of the leaf spring.
DE 297 19 436 U1 teaches a welding apparatus for overlapping welding of foil edges including pressing rollers for compressing the foil edges after heating wherein the pressing rollers are supported on axles wherein at least one axle is movably supported relative to the other axle and vice versa, wherein at least one of the axles is alignable by an alignment device parallel to the other axle and fixable in this position and the alignment device is in particular associated with the movably supported axle. Thus, the axle is supported at two pivot arms wherein the alignment device connects the two pivot arms and forms a bridge between the pivot arms which is disengageably attached at one of the pivot arms so that the attachment is adjustable.
DE 77 00 687 U1 proposes a device for continuously welding webs made from a thermoplastic plastic material that overlap at an edge, wherein the device includes a support for spacing and joining of the web edges to be welded and a heating device for plasticizing the web edges wherein the heating device is supported protruding from a longitudinal side of a housing between the web edges that are supported at a distance from each other and wherein a pressing roller pair is arranged at a longitudinal side of the housing downstream of the heating device, wherein a pressing roller is supported rigid and another pressing roller is supported so that it is displaceable against the spring force, and wherein the heating device is configured as a contact welding skid and advantageously configured as a heating wedge and forms a portion of the support device. Thus, the upper pressing rollers are attached at an upper frame so that they are pivotable independently from each other and so that they are pressable onto the welding material by a common spring. Additional pressure rollers are arranged in front of the pressure rollers on both sides of the contact welding skid in order to press the webs to be welded onto the wedge shaped contact heating element, wherein the contact pressure is advantageously applied by leaf springs and the contact welding skid is configured as a heating wedge that is supported about two pivot axes.